text:
What dictates the prop RPM used during cruise?
I've seen on numerous different constant-speed propeller aircraft and different pilots using different RPMs during the cruise phase on a propeller aircraft. What dictates the RPM used during normal cruise operations, and why is that the case? Often there are multiple possible throttle/RPM combinations that deliver the same power, so where would you pick one or the other?

"Dictate" is the wrong word.  Within the ranges listed in the POH, the pilot may select rpm/MP settings as he pleases to meet other criteria.
Charles Lindbergh instructed many WWII pilots in a technique to extend range, by flying with low rpm and high manifold pressure.  This extended range by reducing the "pumping losses" required to maintain low manifold pressure.  Over long distances this technique did extend range considerably.
Secondly, lower rpm reduces noise - remember that the propeller is the largest contributor to a propeller-driven plane's noise signature.  This is important in the terminal environment where the noise can affect the ground, but it also affects in-cockpit noise regardless of altitude.
This answer does not contradict the former answer, but it extends it to point out that there are other important factors that the pilot should consider in selection of engine operation parameters.

As for noise in terminal environment, you will fly with high rpm there anyway, because high power is only possible with high rpm and you need the power on take off and need to have it available quickly on landing in case you need to go around. Of course you still don't want the noise during cruise for which low rpm is better.

Whereas you should indeed fly with the prop set for high rpm on takeoff, most noise abatement policies call for reduced rpm when you reach an altitude as low as 700 feet.  Also on landing, the prop control is advanced when the power level has been reduced so that the rpm is limited by power developed not by rpm.  Landing in this configuration permits rapid rpm increase if a go-around becomes necessary.

The POH has performance tables (random example: http://www.avsim.com/pages/0310/Carenado/Manual5.jpg) showing fuel burn, true air speed, and %hp, for a given altitude, RPM, and manifold pressure. The pilot selects a performance configuration based primarily on what speed they wish to cruise at, which in turn determines how much fuel they're going to use. Different pilots differ in how much speed they want to achieve, making things somewhat a matter of opinion, but regardless of selection it's standard that the more you pull from the engine, the more harm you do to the engine. Personally, I tend to aim for 65% to 75% maximum horsepower in order to neither overtax my engine, nor use more fuel than is needed.

Note that it's % of maximum continuous power. Takeoff power is generally higher than that (the Katana I fly has a 104% as take-off power)


text:
Is Flight Following in the USA directly equivalent to Basic Service in the UK?
This is partially a question on terminology, I have flown in the USA and used a service which is commonly referred to as "Flight Following".
I have read this question: Is there a European equivalent of VFR Flight Following?
And I am interested in whether requesting a "Basic Service" which I use in the UK is a direct equivalent? If not, what are the major differences?

Comments are not for extended discussion; this conversation has been moved to chat.

Based on the UK Flight Information Services document that Dan helpfully provided in chat, it looks like they're different:
Basic Service

Available to IFR flights in class G
Available to VFR flights in class E and G
Provides information on "airspace activity that may affect your flight"
Pilot is free to manoeuvre as needed, unless otherwise "agreed" with ATC
Provided workload permitting

Flight Following

Not available to IFR flights
Available to VFR flights in any airspace where ATC has radar coverage
Provides information on airspace, traffic and weather
Pilot is free to maneuver as needed, unless otherwise instructed by ATC
Provided workload permitting

So the major differences seem to be:

Basic Service is available to IFR flights; Flight Following is not (it wouldn't make sense anyway)
Basic Service provides airspace information only, not traffic information; Flight Following provides both

The whole traffic vs airspace information thing is very confusing in the CAA doc. Read literally, there's no VFR service that offers both airspace and traffic advisories, but that makes no sense at all. I'm probably missing something, but reading that document makes me glad the US has kept it simple...

To add to that... I assume since Flight Following provides traffic and airspace information then aircraft are positively identified using a unique squawk code? A radar/radar based identification is not required for a Basic Service in the UK.

@BDLPPL That's correct, Flight Following does require a discrete squawk. Do you have a reference for not requiring one for Basic Service? If so, I'll add it to my answer. I Googled quickly and the sources I found were unclear on which UK services require a discrete code.

Very important to note - Basic service in the UK is NOT a radar service and doesn't provide any traffic information (you may get some at the discretion of the controller depending on his workload, visibility and other factors, but it is not part of the service). I'm not close to the US "Flight following service", but based on the  above description it seems the UK's "Traffic service" would be closer.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
What prevents jet engine designs with larger bypass ratios?
In commercial aviation, it seems jet engines grow and bypass ratio increase with newer engines. Here is some examples:

1963: bypass ratio: 0.96 (P&W JT8D)
1970: bypass ratio: 5.0 (P&W JT9D)
1984: bypass ratio: 5.3 (P&W PW4000)
1984: bypass ratio: 6.0 (P&W PW2000)
2004: bypass ratio: 8.5 (Rolls-Royce Trent900)
2007: bypass ratio: 10.8 (Rolls-Royce Trent1000)
2015: bypass ratio: 12.0 (P&W PW1124G)

The bypass ratio has been multiplied by nearly 2 in 30 years (1970 -> 2015).
I understand the need of really high bypass ratio to decrease fuel consumption while increasing thrust. To have big bypass ratio, the high pressure part of the engine must be small compare to the overall size of the engine.

What prevent jet engine designer to design smaller high pressure part or bigger jet engines to increase the bypass ratio?
Is there someone that has made prediction about the increasing bypass ratio in the next decades and written it in a serious article?

Don't forget ground clearance for any of the answer

It's not just about increasing thrust, it's about increasing fuel efficiency.

I'd like to add one more data point to that list - 1955: bypass ratio: 0.25 (Rolls-Royce Conway).

For ungeared two-spool designs, bypass ratios cannot be increased further. Since the fan is coupled to the low-speed turbine, increasing it would overload the turbine. Only if the engine is run at a higher core temperature can the power provided by the low-speed turbine be increased. This would require either better materials (which are not available) or lower times between overhauls (which are costly).
Note that the engines of the Rolls-Royce Trent family have the biggest bypass ratios. Rolls-Royce went with three-spool designs which allow for a finer adjustment of the speed of the different engine components.
When a reduction gearbox is placed between fan and turbine, even a two-spool design can support a larger fan, and this solution will be used in the next generation of P&W engines. Smaller engines like the ALF 502 which is used in the BAe 146 rsp. Avro RJ, used this already years ago to fit a fan to a single-spool engine. For bigger engines, transmitting the enormous power in a compact gearbox was too challenging until now. Just the heat generated by the gearbox of a 200 kN thrust class engine running at 98% efficiency would be almost 400 kW - this needs to be shed somehow!
Another problem remains, however. Bigger fans need bigger nacelles, and their drag increases with the square of the fan diameter increase. Increasing the bypass ratio of a high-bypass engine even further yields diminishing returns, which tend to be compensated by the increased nacelle drag once the bypass ratio grows beyond 12 to 15. To make bigger bypass ratios economical, active laminarisation on the nacelle will be needed.

Are we reaching an asymptote yet? Or do you think we'll see bypass ratios past 15 in the next decade?

How (using what formula or assumption) did you translate "200 kN thrust" into Watts?

@ChrisW: Good question: I assumed that the engine has half as much thrust at Mach 0.8 than static (100 kN), assumed that 80% of this is from the fan (80 kN) and multiplied that with speed (240 m/s). Gives 19.2 MW, and 2% of that is 384 kW. I'd like to know myself if this is correct, but I have heard such values being bandied about for fan gearboxes before.

@RoboKaren: I do not expect 15 in the next decade. Active laminarisation would be needed, and progress there is slow. Eventually, 15 could be conceivable, but maybe in 20 or 30 years. Who knows - predictions are hard, especially those about the future.

Googling "active laminarisation" only leads me to fancy-looking academic papers. Is there an easy way to describe active laminarisation or its effects?

@raptortech97: You suck away the slower parts of the boundary layer through small slits or rows of holes. Once is not enough, you basically make a sieve out of the skin which should be kept laminar. Would make a good question on StackExchange!

I agree with everything except your first sentence, unless you only mean that to apply to the current state of technology. It's quite a large statement to say that it's impossible for ungeared two-spool engines to reach any higher bypass ratios.

@fooot: I qualified that sentence in the rest of the paragraph, and this comes down to "with current technology". You could put a bigger fan on existing engines, but that would not be an improvement overall.

The only way to increase by-pass ratio is to accelerate the high pressure turbine and avoid energy degradation.
To accelerate the high pressure turbine you need higher higher pressure and higher temperature.
A jet engine work like this :
Imagine this : the air have these values (these values are totally arbirtary) 1, 15, 200 (Pressure, temperature, speed), the jet engine Increase pressure in compressor (10, 5, 10) after this the flow pass in combustion chamber (10, 300, 10) with the turbine you transform temperature and pressure into speed (1, 20, 2000) and you pick some energy to rotate the fan.
The fan increase air speed.
So you can increase temperature but all the parts are in metal it's why the manufacturers develop specific alloys and use ceramic foils.
The other thinks to do is avoid leak, the manufacturer develop new abradable material to avoid pressure leak.
The technology venture to reduce mechanical leak during energy transmission to the fan blade.
The new blades profiles (fan blades are twisted) reduce energy leak due to friction and avoid air stall.
In the next year we will see new engine with open rotor and certainly new temperature resistant materials, thus the by-pass ratio will increase (the predictions are 30 or 40).
For open rotor and by-pass ratio see here (sorry i don't have english source)

I'm not as confident as you for the openrotor. There is a noise problem that is easily solved by putting the fan inside the engine. For me, it seems to combine inconvenients of both turboprop and jet engine without combining advantages.

Yes the open rotor is not sale for the moment because of noise but big companies like boeing make work on this, so i believe that this will soon work properly !

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Are there certification requirements for an emergency descent?
In case of emergency, an aircraft may have to descend very quickly. Is there some performance (L/D ratio with full spoilers, descent rate, ...) to be proven in the certification process for such descent?

Emergency descent is just a faster descent, usually the max sink rate the aircraft can safely handle and then level out again.

legal requirements depend on legal jurisdiction. Are you asking about legal requirements under US law?

@RedGrittyBrick I don't know if there is such legal requirement under any jurisdiction. If you are aware of some requirement under US-regulation, it will be welcome, but the question is not meant to be US-specific.

@ratchetfreak it is true that it it is "faster descent", but it is more than that.  Emergency descents are a specific abnormal/emergency procedure and is typically a memory / immediate action item that crew must commit to memory (e.g. seatbelt signs on, cabin crew notify, thrust idle, spoilers max, at 250 KIAS -- gear down, descend with speed hold 250 KIAS)

There is a descent requirement, but it's perhaps not in the way you imagine as it has to do with oxygen supply. FAR 122.333 subpart K states:

(b) Crewmembers. When operating at flight altitudes above 10,000 feet,
  the certificate holder shall supply enough oxygen to comply with
  §121.329, but not less than a two-hour supply for each flight
  crewmember on flight deck duty. The required two hours supply is that
  quantity of oxygen necessary for a constant rate of descent from the
  airplane's maximum certificated operating altitude to 10,000 feet in
  ten minutes and followed by 110 minutes at 10,000 feet. The oxygen
  required in the event of cabin pressurization failure by §121.337 may
  be included in determining the supply required for flight crewmembers
  on flight deck duty.

This specifies that a turbine aircraft must be able to descend from it's maximum certificated altitude to 10,000ft in 10 minutes or less. This means the maximum descent speed is variable to maximum certificated altitude, so if an aircraft's ceiling is 42000ft it must be able to descend at least 3200fpm, it it's 25000ft then 1500fpm.
As for how that's done I don't think the regulations say, it's up to the manufacturers to develop aircraft that can meet the requirement.

And there is the implied requirement of being able to level out at 10k ft

I'd prefer it that way for sure.

@ratchetfreak I'd say it's probably pretty hard to spend 110 minutes at 10,000 feet if you don't level out from the descent around 10,000 feet.

In addition to oxygen supplies, there are also regulations about cabin pressure. The descent rate required can be determined by the probability of decompression.
FAR §25.841

If certified to operate above 25,000 feet, cabin pressure altitude must be less than 15,000 feet "after any probable failure condition in the pressurization system."
For "any failure condition not shown to be extremely improbable:" the cabin altitude is limited to 25,000 feet for 2 minutes, and is not allowed to exceed 40,000 feet.

So for any "probable" failure, the aircraft must be able to descend to 15,000 feet before the cabin pressure is completely lost. For any failure not "extremely improbable," the aircraft must be able to descend to 25,000 feet within 2 minutes of losing all cabin pressure.
These probabilities are:
Probable: more than 10-5 (1/100,000)
Extremely improbable: less than 10-9 (1/1,000,000,000 or "not anticipated to occur during the entire operational life of all airplanes of one type")

I think it should be "for any improbable failure". Extremely improbable is what the requirement excludes altogether.


text:
Can a Rutan Quickie be made into a legal Part 103 Ultralight?
I was was thinking about buying a 80s rutan quickie q-1, it has a 18 hp motor. I want to get a ultralight but I like this one because it is fast. Can I get a motor that would be within the requirements? I don't know how I would be able to make this an ultralight. Iwas wondering if a Rutan 277 engine would work well in it and if this would be in the requirements

Possible duplicate of Is it possible to fly using a small engine?

Hi, welcome to aviation. I have tidied up/reworded your question and have hopefully kept the important parts of your question. Please have a look at the [help] to find out more about asking/answering questions here.

If you don't get a good answer here, you might try quickheads.com. Because there are so many possible variations of kit aircraft, it's often useful to ask people who have actually built them. In general, builders/owners associations are a really good source for "could I do this?" questions.

You need to specify which country you're talking about, because the meaning of the word "ultralight" varies dramatically from country to country. In the United States, ultralights must weigh less than 254 pounds; in Brazil, they can weigh 1,500 pounds.

I edited your title to more closely match your actual question -- if that isn't what you're trying to do, feel free to roll it back (once it's passed peer review).

I doubt the Quickie would fly well enough at very slow speeds to meet the rest of the Part 103 requirements -- specifically, the limit on maximum level flight speed.  Limiting fuel capacity is easy, and the 18 HP original engine worked well enough on the Q1 -- but it was a lot faster than 55 kt (close to double, as I recall).  From comments (thanks, Gerry) I understand the Q1 has a stall speed of 42 kt -- fairly reasonable for a light aircraft, but well above Part 103 maximum of 24 kt.
You might be able to slow down enough by installing a flatter-pitch propeller, but that would have other effects (overspeeding the engine, for instance) that would need to be addressed, and then you'd be trying to fly with almost no speed range -- 42 to 55 kts isn't, IMO, a safe performance envelope (and yes, the Q1 would still go faster than 55 kt in a dive, but the level flight and climb performance are where the safety issues lie in this case).

It won't meet the 24 kt maximum stall speed requirement of Part 103.1(e)(4) even if you could find a way to make it slow enough without destroying the flying qualities.  The published stall speed of the Q1 is about 42 kts. Having helped a friend build one, I can say this is not what you want if you're looking for an ultralight.  It could however qualify as an LSA.

does anyone know of a ultralight thats afordable, that is a closed cockpit. Because all these ultralights im seeing are kinda ugly, lol

@Blackhawk19 There are several -- but this forum isn't set up to answer that question, even if you ask it as a proper question (shopping questions are generally OT on Stack Exchange sites).  Might want to ask in chat or on a discussion forum.

@Blackhawk 19: Beauty is in the eye of the beholder, of course, but most of what you seem to think is ugly in ultralights is a consequence of needing low weight, top speed, and stall speed to qualify as an ultralight in the first place.

@Blackhawk19 and not to mention that there are a number of ultralight legal aircraft that I find quite graceful and pleasing to the eye.  Look for the ones with composite structure and skin -- like the Carbon Dragon sailplane.

Have you looked at the Quicksilver 500?  It's a 2 seater with enclosed cockpit.  http://www.quicksilveraircraft.com/gt500.php  Might not be Part 103 compliant. It does look pretty sharp.

GT400 is similar, but only 1 seat  http://www.quicksilveraircraft.com/Enclosed_Cockpit.php

If it had a lighter engine, the wing loading would be slightly smaller.  If it could be rewinged (longer chord and more camber?), then it might work.  You could get enough lift at a slower speed.  A bigger wing would weigh more, but perhaps that would be offset by the lighter engine.  Of course, the CG would change and the wings would need to account for the shift in cg.

If you are not Burt Rutan, Gene Sheehan, or Tom Jewett, then you probably should not modify a Q1 to that extent. You would be moving into the realm of designing a new ultralight, which does not seem to fit in with OP's goals.

Speed is not just about the engine. The reason the Q1 is so fast on an 18HP engine was that it had high wing loading, to put it a simple way it has to fly faster for the wings to produce enough lift. Its stall speed is about 41 knots, which is a characteristic of the wing shape and area, if you put a smaller engine on it you won't change the characteristics of the wing.


text:
How do ground effect vehicles perform turns?
Considering that Wing-In-Ground-Effect (WIGE) vehicles fly with a rather low ground clearance, there is not much room for banking. How do WIGE vehicles turn? Do they turn just very slow with a low bank angle? Or do they turn uncoordinated with wings level?
I can imagine that banking has an opposite effect: the raised wing has less ground effect so more drag so it creates some countering yaw moment. Is this correct?

"carefully" ....

Wouldn't the raised wing have less drag, because it's experiencing less ground effect, ergo producing less lift, ergo generating less induced drag?

@Sean, no: the essence of the ground effect that you get more lift for the same drag. Or same lfit with less drag. Also, if you are in a sustained banked turn, then by definition both half-wings produce the same lift - otherwise you'd be rolling with acceleration. It follows that the surface that is less in ground effect will have more drag. (Plus there are usual effects due to ailerons position etc. - which usually contribute with the same sign).

It turns like an airplane by tilting the lift vector. Watch carefully in this video, especially about 50 seconds in, and you can see the craft is turning by banking.

It just can't bank very hard unless it climbs a little higher. This is one of the problems of GE aircraft; they aren't very maneuverable because they can only make gentle turns at the normal cruising level close to the surface.
The alternative to banking, if you don't have enough room to roll, is skidding, where you are redirecting the thrust vector and also generating some lateral force from the sideways presentation of the craft's body. Basically like a hovercraft. A lot less efficient though because of the drag rise from the skid. Some of those really big GE machines like the Ekranoplan would have used skidding (kind of obvious from the huge rudder that it's designed to skid) and maybe a little bit of bank.
It's probably a good thing that this concept has not been all that successful. If the world was full of these types of machines crisscrossing every which way over oceans and lakes, all at the same level and going pretty fast, you probably have a lot more mid-airs than you get with airplanes, or boat collisions for that matter.

How did large versions like the Ekranoplan turn? Looks like there's a fairly large rudder, and engine thrust might have been used. There doesn't seem to be much margin for bank angle.

It never occurred to me that such craft would indeed "meet" - just like ground vehicles!  You'd need stop signs and so on.

@rcgldr thanks for the mention I added an extra paragraph to address that.

Stop signs on buoys! That would be rather funny, @Fattie!

@FreeMan - right  :)


text:
How can larger wingspan decrease the strength of wingtip vortices?
In the last paragraph from the link below, it states that Vortex Strength is inversely proportional to Wingspan. Why is this?
http://avstop.com/ac/flighttrainghandbook/wingtipvortices.html
EDIT: From https://howthingsfly.si.edu/aerodynamics/vortex-drag: "The farther a vortex is from the main body of the wing, the less influence it has on the wing."
Again: why?

The strength of the wing tip vortices depends upon the pressure differential between the top surface and the bottom surface. In general larger heavier planes produce stronger vortices.
Now consider two planes with the same weight but one with shorter wing span and one with longer wing span. The pressure differential between the top and bottom surfaces of the wing for the plane with the longer wingspan will be less ( pressure=force/area). Thus the strength of the wing tip vortices for the plane with the longer wingspan will also be less.

An accurate comparison should assume the lift coefficient of the wing is the same, not the total lift.

Wingtip vortices, as from the wake rolling up at the wingtips, become larger with increasing lift and decreasing aspect ratio. At equal wing area, the low aspect wing must deflect the airflow to a higher angle, relative to the free air stream.

For a useful comparison, we need to ensure each wing has the same lift coefficient $C_L$. As span increases, assuming chord is constant, then the wing area and aspect ratio ($A$) also increases proportionally. Since wingtip vortex strength is related to the induced drag, you may have seen this relationship:
$$C_{D_i}=\frac{C_L^2}{\pi e A}$$
The larger the span, or aspect ratio, the smaller the induced drag (i.e. wingtip vortex) for the same lift coefficient. But why?
From the circulation theory of lift, any change in the circulation along the span will shed trailing vortices. In turn, these trailing vortices will induce downwash on the wing span. At the wingtip, the downwash rolls over and creates the wingtip vortex. Now if the span is short, the change of circulation will be larger, thereby inducing higher downwash all along the span, and the rollover at the tip will be stronger. If the span is longer, the change is circulation is gentler and less downwash/wingtip vortex is induced.
In the limit where the span becomes infinite, assuming the same $C_L$ for the whole wing, the circulation distribution is stretched to a constant value, such that the change in circulation along the span is zero, then no trailing vortex exists and the induced drag becomes zero as well.

It's because the "leakage zone", where air is flowing around the tip, is smaller relative to the total wing area if you add more span without increasing chord.
Best way to visualize it is to take it to the extreme; look at a sailplane wing, where the area of the wing tip is a pretty small area in relation to the total area, so the leakage and resulting vortice is much smaller relative to the overall package of air displaced by the wing.
In other words, more span takes you a little bit closer to the theoretical infinite span wing that has no vortices at all because there is no tip.
Of course, adding span without reducing chord adds wing area.  If you want to compare tip losses of two wings with the same area, they should really be talking about aspect ratio.


text:
Is moving payload masses during flight to restore mass centering, or to avoid having to trim, a useful approach?
Note: Title was previously "Movable big missiles/bombs/tanks under fighter jets: conceivable?"
Example: lateral weight distribution in fighters
Fighter-bombers jets are small and lightweight in proportion to the under wings load (including payload but also external tanks) they carry which means most stuff can't be placed right below the body of plane and heavy payload (very big missiles and bombs) ends up relatively very far from the center of mass.
(Although some designs have a bay to hide payload, the bay is small compared to the maximum possible load of other fighter and they still have the option to carry under the wings.)
So here is a (possibly unworkable) idea:
Is it conceivable to mount heavy load on movable arms that can move weight left or right to adjust mass centering:

at under wing load installing time?
during fight?

The heavy load, including external tanks, would be automatically moved to preserve mass balance.
Example: longitudinal balance for cargo planes
The idea here is to move the fret of a cargo plane in the longitudinal axis, to adjust balance and minimize trim.

Comments are not for extended discussion; this conversation has been moved to chat.

I couldn't find the reference but I think there's a movable ballast on some military transport to restore balance after some heavy payload is air dropped.

Lookup the concorde trim tank which is close to what you are looking for. Note that the scaling effect works against your favour on a smaller fighter jet

While I don't know of any airplanes that move load in flight for CG purposes, there are definitely airplanes that have various fuel tanks that can be used to trim the airplane during flight. Some of these systems will move the CG aft after takeoff for better performance in cruise, and then move the CG forward before landing for a more stable approach and landing.

Why worry about any of this? In a steep turn, the best place for the underwing stores is evenly distributed about the centerline, same as in wings-level flight.
Are you trying to address the situation where some stores are dropped and others are not?  Aileron trim should be be sufficient to address this issue.

The worry is the asymmetric load if some reason heavy bombs and long range missiles are not used in pairs.

And we have been trying to tell you that you can use rudder and aileron trim to compensate for asymmetric loads!  If it was a serious problem the best minds in the military industrial complex would have come up with a solution sometime in the last century.

@MichaelHall "Clever people would have done that already if it was a good idea" is not really a good and helpful answer in general.

Off the top of my head, I can only recall one airframe + munition combination where this was an issue, and that was the attempted Harrier Harpoon load-out: if I recall correctly it couldn't fit a single missile on the centerline (clearance) but it could just about lift off with two... but it couldn't land with only one under a wing (asymmetric lift), meaning it would have to bring a dummy weight or always fire both, which killed the idea.

@curiousguy, I didn’t answer, that was a comment.  You are worrying about something that isn’t a problem.


text:
What does it mean for a ATC to say a flight's callsign followed by "in disguise"?
So I'm just a aviation fan without industrial background.
I'm listening to Kennedy Steve's ATC communication and he said more than once like "American 600 in disguise."
What does it mean "in disguise" in this context?
Thank you.

Can you link to where you heard this?

I believe it’s https://youtu.be/l9zQr_7KkoQ but I can’t remember the exact time now

Kennedy Steve has a whole seperate section in the pilot-controller glossary :D

@Lionet Chen https://youtu.be/l9zQr_7KkoQ at 1:36

The controller was probably referring to an airplane in a different livery but operating under the American call sign.
A likely example is US Airways. After the two companies merged, from October 2015 all flights were operated under the American call sign, but re-painting the US Airways planes took at least a couple years.
This is not standard phraseology but "Kennedy Steve" is known for trying to inject some humor into his work. See also: What does Top 1% mentioned by ATC refer to?

Thanks. I thought it was a standard postfix like “heavy” that actually gives information :) now I know. The same clip has a dinosaur reference, which I believe is also a metaphor, not an airliner company

"Dinosaur" could mean almost anything in Steveish: a really old plane, a plane with a dinosaur logo, a giant plane or something else. Hard to know without seeing video of field at the time.


text:
How are fuel injectors in a jet engine monitored to detect malfunction?
As far as I know in a car engine the ECU can adjust fuel mass flow through every injector. I don't know the exact algorithm but probably engine roughness is monitored. Of course this is not possible in a jet engine. What will happen if an injector starts to malfunction? I assume it will be quite difficult to detect and a slight decrease in maximum power will appear. But engines usually are not run at full power? Can this be dangerous when maximum performance is needed (like engine failure at V1)? How are injectors tested in engines with mechanical fuel control? Can FADEC monitor fuel injectors?

Car engine ECU's use a few sensors to adjust fuel flow. One is the MAF (Mass Air Flow) or MAP (Manifold Air Pressure) and the other is the Oxygen sensor in the exhaust stream. Combined with other engine data (RPM and throttle) an injector timing (opening time of the orifice) is calculated from a 3-D lookup table programmed into the ECU. This is significantly different from how jet engine fuel injection systems work. Jet engines don't have cycles, so its a continuous flow system.

I know that but I was talking about different think. Car ECU can try compensate for individual injector wear or different calibration and try to compensate accordingly.

According to the AgentJayZ YouTube channel, which has videos of fuel nozzle testing, the injectors are not the same as those in a car. A car's injectors open and close in response to an electrical signal. The fuel nozzles in a jet engine are just nozzles, with no moving parts. The fuel flow to the engine is regulated by adjusting the fuel pressure.

"Car ECU can try compensate for individual injector wear or different calibration and try to compensate accordingly" No, it really doesn't, there is no "injector wear compensation" in an ECU (I've written ECU software). It works on timing tables. The injectors are opened for some period of time using a PWM signal based on the sensors I mentioned. It can't compensate for wear or even knock (which is why a knock sensor produces a check-engine light). There is no way for the ECU to measure how much fuel each injector is providing, its based off of factory calibration.

I've never worked on a turbine that had any sort of monitoring of injector/atomizer performance. I suppose that in theory it could be possible to do so by monitoring fluctuations in fuel flow, but the aircraft I worked on never had anything like that.

Fuel nozzles are overhauled and bench tested to meet the manufacture's operational limits.  They are controlled for both flow (back pressure) and also flow pattern.  The FADAC monitors fuel flow, this along with the compressor vane position are the main input controls for thrust generation.
The fuel nozzles do degrade during engine's operation.  This contributes to the engine running hotter as it ages.  Other contributors are the erosion of the compressor hardware and the burning/oxidation of the combustion chamber and turbine hardware.  In fact a defective fuel nozzles may lead to a "hot spot" that accelerates the burning/oxidation of the combustion chamber.  The FADAC and flight crew will monitor the throttle response and also the Exhaust Gas Temperature (EGT) as the controls to understand the relative health of the fuel nozzles.  If the engine exceeds the EGT limit a mandatory boroscope inspection is required to keep the Aircraft in service, this inspection will visually verify the condition of the fuel nozzles and combustion chamber.

Yes a FADEC can monitor fuel flow.
Let's assume you are operating a simple turbine.  Normally you will have fuel flow, turbine speed and if a turboprop a torque monitor.  The pilot monitors each of the steam gauges. The fuel control unit will normally limit max fuel flow.
An ECU is more akin to a FADEC, and the range of programmatic control in a FADEC is diverse, so a generalization is not as easy as in a simple turbine.
So to summarize, Yes, a FADEC can monitor fuel flow (and everyone I am familiar with does).  And in the case of a more simple turbine application, the pilot, and the fuel controller (which will vary in implementation) can also provide limits.

The question is asking about individual injectors, not total fuel flow.

@RalphJ … and since the injectors are just fixed nozzles, total flow and pressure is all you really need to know.


text:
What are the differences between these types of air cycle machines?
I am MSC student of mechanical engineering and my project is about ACM machine. I have read something about various systems of air conditioning system in aircrafts;

simple system
boot strap
reduced ambient temperature
regenerative system
boot strap with evaporator
simple system with evaporator

I just know that reduced ambient temperature is for supersonic aircraft.I don't know other systems applications.For example, when is a regenerative system used and when boot strap is used?
Are all of the possible air conditioning systems exists in every aircraft and switch to another depending on flight condition?

Two related questions. How hot would pressurized air get if the air conditioning failed? and Why is there a compressor in an air cycle machine?

Really not sure what you're asking, nor do I know what these terms you've found mean, so let's start with these drawings and see where we end up.
DC-9 Bleed air enters from the engine (or APU) at bottom left of this drawing and enters the primary heat exchanger. Then it enters the compressor in the ACM and then on to the secondary heat exchanger. From here it enters the turbine and this is the point that the heat loss occurs and cold air enters the water separator and then the cabin of the airplane.
Note the anti-ice screen and the pack anti-ice valve which adds a little heat if the air exiting the turbine is too cold and is causing ice.
The water separator is a cone-shaped cage with a heavy cotton bag over it. This collects condensation in the air and dumps it on to the face of the secondary heat exchanger to cool and improve it's efficiency.
Temperature in the cabin is controlled by the temperature control valve on the left side of the drawing.

737 This system is very similar to the DC-9 and really the main difference is that the pack anti-ice valve here is operated electrically, while on the DC-9 it is done mechanically with a pneumatically operated valve.

757/767 This is a much different system, many more electrical sensors and control. The pack cooling fan is an integral part of the ACM, where on the other two systems they are separate components. The water separators are much more advanced and don't require regular maintenance like on the other systems.

As you can see, these three systems are all basically the same with the only real difference being how they are controlled and some of the ancillary components.

thanks alot for ur answer.in this link there is different types of aircraft refrigeration system and its basic consepts my question was originated from this book. https://books.google.com/books?id=JyGeRoZIy80C&pg=PA391&dq=aircraft+refrigeration+system&hl=en&sa=X&ei=DJ9oVbcPhIBTiIaA8AI&ved=0CB4Q6AEwAA#v=onepage&q=aircraft%20refrigeration%20system&f=false

You're welcome. Thanks for the link. It seems then that these 3 systems are 'Bootstrap'.  The text in the link says a bootstrap can't be used on the ground, however, each of these systems has a cooling fan in the ram ducting so that they can be used on the ground. The DC-9 and 727 use electric fans, the 737 has a pneumatic fan and the 757/767 has a fan driven by the ACM itself.

yes.im curious to know when regenerative cooling or simple system with evaporator is applicable?  it is mentioned for supersonic flights ram air isnt usefull solely and there should be external turbine to cool the ram air for heat exchanger .my professor offer me to search about this topic(acm machines systems in aircrafts) and ask me to propose him detailed subject about it to work on it as my thesis .i generally know something but not in detaild. im wondering if you give me detailed subject to work on it as my thesis .thanks again

in this book there is more detailed information https://books.google.nl/books?id=ZiDbFhFk-AYC&pg=PA80&dq=aircraft+refrigeration+system&hl=en&sa=X&ei=eaZoVY3zCoScsAG7woC4CA&ved=0CCcQ6AEwAQ#v=onepage&q=aircraft%20refrigeration%20system&f=false

Sorry ghlam, I don't know why you would choose one type of system over another. As for supoersonic maybe something at this site might help. http://www.heritageconcorde.com/#!concorde-air-conditioning-group-descript/c252t Reading over the description it all sounds pretty standard and not overly exotic.


text:
Why do holds at or below 14,000 feet have different procedures?
When holding at or below 14,000 feet, the time for each leg is 1 minute. However, above that altitude, the legs are flown for 2 minutes, and the turns for 1 minute and half.
Are these differences due to airspeed, or any other recommendation?

The reason for a different turn rate at higher altitude is because of the physics of Indicated (IAS) and True (TAS) airspeed. Many aircraft would find it impossible to do a standard rate turn at high altitudes.
A standard rate turn is 3° per second. This is also known as a two-minute turn because it would take 2 minutes to make a full 360, or 1 minute for a  180°, like each end of a holding pattern.
The bank angle required to make a 3°/sec turn is a function of TAS and bank angle. The formula is:
$bank\,angle =\frac{turn\,rate\cdot TAS}{1091}$
So a standard rate turn at 170kn TAS requires a bank angle of 25°. As bank angle increases so do load factor and stall speed. A 25° bank yields a 10% increase in load factor and a 5% increase in stall speed. For this reason FAA and ICAO regulations require holding patterns to be standard rate, but not to exceed a 25° bank angle.
Here's where the altitude enters the equation. The relationship between TAS and IAS is dependent on air pressure and density. At 5000 feet in standard atmosphere an IAS of 160kn yields a TAS of 170kn. A standard turn at 170 KTAS would require the maximum bank angle of 25°. But in the thinner air at 14,000 that same 25° bank at 170 KTAS is only 142 KIAS.
So as altitude increases, a standard rate turn requires a slower IAS and a higher bank angle. At higher altitudes it would become impossible for many aircraft to make a standard rate turn without stalling. So at 14,000 feet the required turn rate is decreased to 2°/sec, which is a three minute turn (thus 90 seconds for a 180°). Where a standard turn at 14,000 IAS is limited to 142 KIAS, a 3 min turn can be performed up to 212 KIAS.
This is the reason turn rate must be lowered at higher altitudes.

I gave up on trying to figure out why the designers do what they do. However, here’s a guess on this one.
If you are holding below 6,000' you are most likely on an approach to an airport or holding at the missed approach point. By limiting speed to 200kts and legs to 1 minute the protected area is much smaller. Often you will also see a note on the chart limiting the distance from the holding fix. The designer can make the hold closer to the airport elevation which makes the approach easier for the pilot. The purpose of the hold on an approach chart is for a course reversal or missed approach. On other forums, general aviation pilots have stated that they have never, or almost never, been given a hold for spacing when on an approach.
If you are holding above 6,000' you are most likely not a Cessna 152—you are probably in a much faster airplane. So the protected space needs to be substantially larger. That’s why the airspeed is limited to 230 kts between 6,001' - 14,000’ and legs are 1 minute 30 Seconds.
Above 14,000' you are probably an airliner or business plane that is holding for spacing purposes. The highest mountain peak in the continental US is 14,505' and we know that in mountainous areas the MEA is 2,000' above the highest obstacle. So a hold along an airway has 4 miles on the holding side already protected. And outside of California and Colorado there is plenty of room. ATC can have an aircraft hold without worrying about them hitting the ground. But limiting airspeed to 230 kts and making legs 1 minute 30 Seconds makes it easier to ensure that the airplane won’t hit anyone else.
Holds used to be much more common in the US airspace but the FAA computers do a much better job of estimating traffic and the implementation of ground stops and EDCTs has made them much less common than in the past. From what I have read on other blogs, they are mostly used for unanticipated weather delays.


text:
Is there a name for the area for aircraft to back track near the runway threshold?
Some airports have an area, on the threshold, used to back track the aircraft, mainly because of the their wingspan, they look like a half wheel.
Is there any designation for this area?

Can you provide an image depicting what you describe?  As it is I cannot tell what you are referring to.

You have received answers for the US. In France, this is sometimes named a raquette, as it has the form of a tennis racket. See here, in French (image at the last quarter). Officially reversal area.

I don't know if it is official, but across Europe, Middle East, Asia, and north Africa I hear using "turnpad", and many ATC in these regions provide directions like "bactrack via turnpad and continue taxi via taxiway A", that means go ahead to turnpad bactrack and vacate runway via taxiway A.

It sounds like you're talking about these:

I'm not sure if the designation is "official", but pilots in the US (and the FAA in various documents) usually refer to such areas as a "Runway Turnaround Area" or simply "Runway Turnaround".
Their purpose is to allow aircraft which have back-taxied on the runway (or landed and rolled past the taxiway turn-offs) to turn around to position for take-off or return to a taxiway turn-off.

Note that the "runway turnaround" is distinct from a "run-up area": The runway turnaround is considered to be part of the runway, so an aircraft occupying that area is occupying the runway. A run-up area is generally a distinct area, usually off a taxiway, where aircraft can perform engine run-ups prior to entering the runway.

When you say that a runway turnaround is part of the runway, is that true in all cases or is there any variation? I noticed that in the picture you have there, the runway edge lines actually extend into and encompass the turnaround, but at the airport I've most commonly flown out of, the turnaround is not included within the runway edge lines and the local pilots seem to treat it as if it were not part of the runway. That is, it's not uncommon for one plane to be going through its before takeoff checklist there while another aircraft lands.

@reirab The airport's markings are probably the decisive reference, but I've never been at an airport where the turnaround wasn't considered "part of the runway". Of course in my experience they've also always been on the "runway side" of a hold-short line (and at least for ATC purposes when you cross that line you're occupying "the runway") -- there are probably more shades of gray to this at a grass field, or one where you're not crossing a hold-short line on your way to the pad.

@reirab, would you tell us the airport and runway so others can see what that area looks like for comparison?

@BowlOfRed Hmm... I think I'll just post a question on it, so it doesn't blow up the comments here.

@BowlOfRed I've posted the question with pictures here.

Perfect answers! Thanks a miliion,


text:
Why are many military fighter aircraft designed to fly supersonic?
It is my understanding that these aircraft rarely fly at supersonic speeds anyway—the ordnance they carry, the increased fuel burn (even with supercruise), and the increased chance of detection make supersonic flight either hard to maintain or seem unnecessary. In addition, it would seem more beneficial to perform subsonic evasive maneuvers against an incoming missile than to try to outrun it (many air-to-air missiles fly at Mach 3 or higher). Finally, the subsonic Sea Harrier even downed a supersonic-capable Mirage III and many supersonic-capable IAI Daggers to no losses during the Falklands War. Though this can be attributed to the superior pilot training and offensive technology of the Harriers, how come many other aircraft were/are produced with a supersonic requirement?

Related topic and at least partial answer here: http://aviation.stackexchange.com/questions/17247/request-for-intercept-geometry-explanation

Interesting, that the answers gathered here are in conflict with the answers on this question: http://aviation.stackexchange.com/questions/21987/why-is-the-maximum-speed-of-current-fighter-aircraft-lower-than-those-from-the-1/21988#21988

One reason is interception (with interceptor, not missiles).
Defence is probably more important. Defence with fighters is still important for three reasons:

There are relatively effective counter-measures against surface-to-air missiles. A fighter pilot can adjust the strategy to the counter-measures encountered, missile can't.
In peace or limited conflict situations it is often not known whether a suspicious target is hostile at all and the only way to identify it is to have a fighter fly to it and have the pilot identify it with their eyes.
Fighter can also do other things than use lethal force. In peace time you generally don't want to shot down an intruding military aircraft of another country straight away. Fighter can chase it away from your territory or can try to arrest it (force it to land on your own airbase). And fighters are also used to identify and possibly navigate to safety civil aircraft that lost radio contact.

So when a potentially hostile aircraft is detected entering your territory, fighters are sent to intercept it and help it, arrest it or shot it down depending on what it turns out to be.
If the fighters are slower than the intruder, they may not be able to intercept it at all (they don't usually know where it is flying so they can't wait for it). The faster they are, the larger area they can defend. In this case the interceptors take off without external fuel tanks (as they won't be flying very far) and with only relatively small air-to-air missiles, so they can fly fast.
Conversely if you try to penetrate the enemy territory, flying faster limits the number of fighters that can intercept you. However in this case it is more useful to rely on stealth or flying low to evade detection, so attack aircraft often are either not supersonic or have lower maximum speed.

Thanks, that cleared it up a lot for me. For some reason I believed that intercepting was no longer common but a quick look anywhere proved me wrong.

@L3R5, actually, I completely forgot to mention (rewrote the answer now) the most important reason to have a piloted interceptor up there: often you don't know that something is enemy plane. All you know is it is a plane that does not report itself and you need the interceptor to identify it first.

I see! I heard that an initial problem with BVR fighting was identification. I think during peacetime, visual recognition is required before any action is taken. Not sure about wartime.

@L3R5, I believe they did some BVR interceptions in both first and second Gulf war just based on radar signature identification from AWACS. But even there they were not able to identify all targets by radar only and unlimited war is rather rare these days and in the limited conflicts you always have to be careful not to shot down civil aircraft.

The Iran Air 655 shootdown would have been avoided with fighter intercept. There was a carrier nearby but unfortunately the carrier was not in direct radio contact with the Vincennes, the ship that fired the missile. The carrier captain was not willing to send his pilots in without being able to let the Vincennes know they were coming. Sadly they could not take advantage of it but that illustrates what @Jan was saying about the advantages of speed. They can't come to the rescue if they can't get there in time.

@L3R5 Interception is particularly topical in Europe at the moment. The Russian Air Force is flying a lot of missions right up to the edge of NATO countries' air space, turning parallel to the border right at the last minute.

I don't think anyone is going to fire a warning shot.  The moment the gun flashes, or there is smoke in the air, that is going to be considered a lethal action and someone, somewhere, is going to die.  Nothing will escalate a situation more than shooting in your direction.

The answer, speed is life.  While that may seem abbreviated, superior speed gives fighter aircraft far more options to attrite the enemy or to survive another day.
The following is a limited subset of general reasons why having superior speed would be an advantage, but unfortunately, specifics are beyond the scope of this discussion.
Pure Speed

Offensively, speed is necessary to consummate an intercept, although, it often does not require superior speed, as geometry is a far more useful intercept tool.  However, offensively, speed becomes more useful when chasing down a fleeing aircraft, or when flowing to multiple targets.
Defensively, speed can help targeted aircraft bug out, as well as simply increase time to kill so that other friendlies can swoop in and save the day.  You burn far more gas exploding in a fireball than you do dumping fuel into the afterburners!

The Power
However, the power to go fast is often just as important, if not more important that the ability to go fast.  Those afterburning, fuel guzzling, engines allow fighters to have enormous rates of climbs, and to sustain airspeed through much more dynamic maneuvers than slower, less powerful, aircraft.  Thrust to weight ratio is paramount in a turn rate fight, and, in BFM, the ability to suddenly add a fist full of knots may be the deciding factor between missile giver and missile taker.

Thanks for the great answer. It makes a lot of sense now--a team would be at a serious disadvantage if they could not help each other. I wish I could select multiple correct answers!

Another Addition to the previous answers would be:
Most maneuvrability/performance theories are based on the Energy of the aircraft. So the higher and faster you fly, the more Energy you have for combat. You can convert this speed in altitude for example. This was especially true for military aircraft in WW2.
For example:
https://en.wikipedia.org/wiki/Energy%E2%80%93maneuverability_theory

To add to other answers, aircraft speed and altitude greatly contributes to missile kinetic performance. The range difference between a missile fired at mach 1.6 at 35k feet versus the same missile fired at mach 0.5 at 10k feet is (tactically) massive. Also faster fighters will generally climb faster while covering greater distance which is important for interception from ground scramble.

An interesting point, which would be much improved by providing specific examples of a missile type fired from low altitude and low speed to higher altitude and higher speed.


text:
Is it plausible to forget the cockpit unlocking code?
Is it plausible for a pilot inside the cockpit to be incapacitated and that at the same time the pilot locked outside simply doesn't remember the code or the procedure for entering the cockpit?

I would speculate that the answer here is the same as the answer to "Do you forget your banking PIN or the procedure for making a withdrawal?" -- People can forget ANYTHING (human memory is very unreliable), but we do tend to remember things that are important to us or that we do frequently - and presumably gaining entry to the cockpit is both important to a pilot and something they do frequently :)

@voretaq7 Maybe it is silly, but I reasoned that when there are two pilots during a flight and one is outside and needs to enter, he can always rely on the other, so it can be that he doesn't know the code...

That may not be a good assumption -- This was discussed a little bit in chat and basically there's no way for the person inside the cockpit to know if the one outside really forgot the entry procedures or if they're saying they forgot because someone has them at knifepoint trying to get one of the pilots to open the door. In that situation the safest course of action is to keep the door closed anyway…

Also related: The answers here & on the duplicates

@voretaq7, the pilot outside the cockpit needs to knock "7500" so the pilot inside knows he's been hijacked. (3/4 in jest...)

@FreeMan This also works.

The code would also be shared among the purser and/ or the other flight attendants, so the answer is no. I believe however that they tend to keep the same code for a few days within the same crew to make remembering it easier.

Perhaps you might explain who sets the code, and whether it is tested (by someone else) after being shared by that person with (the) others?

From the press conference Lufthansa gave on March 26, or sounded like they all have the code ready to quote when they are being woke up at midnight. It sounded though as if the code was never or rarely changed, but I guess that was more a poor choice of words then the truth. The code must be changed every now and then.

@Maverick283 "Every now and then" may but refer to quite a long period. After all even a leaked code can be ovrerridden from within the cockpit.

@HagenvonEitzen I know hence a comment and know answer and I simply have no idea at all in which interval this code is changed.

Does it mean you need to re-learn 7-digit numbers again and again, knowing that probably you won't ever need them even once in your life?


text:
What is ETOPS and how does it work?
According to this press release by Boeing earlier this year, the 747-8 has received its ETOPS 330 rating. This is required by all 4-engined planes made after February 2015 to fly beyond 180 minutes from an en-route alternate airport.
Does this apply only when one engine has already failed? I understand four-engine jets usually continue to their destination on three engines. And how does this compare to the 747-400. Can it fly ETOPS 330+ routes? I remember them doing missions that twin-engine aircraft couldn't because of their lack of ETOPS.
A follow-up question for those who are interested: Why does ETOPS not apply to older 4 engine aircraft?

There is something wrong if Extended Twin Ops (or Extended-range Twin-engine Operational Performance Standards if you wish) are forced on four-engined planes.

@Monolo Well, according to the press release, they have applied to four-engined planes since February this year. If you want to ask about why, that's a separate question.

ETOPS = Extended Range OPerationS

I assume that a 747-8 can at least fly stable in the air with two running engines at one side:  http://aviation.stackexchange.com/questions/11582/can-the-airbus-a380-safely-fly-with-two-engines-out-on-the-same-wing/14622?s=17|0.1050#14622  What happens with on running engine? Are they forced to decline slowly?

I also find it strange that the 747 has the same ETOPS as the 787. Both 330 min.

330 min is good enough to cover the entire Earth except for an area of Antarctica and ocean south an area between Africa and Australia (see http://www.gcmap.com/mapui?MS=bm&PW=2&DU=mi&E=330). For any practical purpose, 330 is enough to go anywhere you'd like to go.

Your title asked a question different from the body, and it sounded like you knew the answer to that question, so I have updated the title to match.  Feel free to change it if I have misunderstood your intent.

@Lnafziger I see what you mean. Although I do know what ETOPS is (in general) I'm interested in knowing why the 747-8 requires it while the 747-400 apparently does not.

@ZachLipton The Airbus A350 has an EASA ETOPS of 370 min. (http://www.airbus.com/newsevents/news-events-single/detail/easa-certifies-a350-xwb-for-up-to-370-minute-etops/)

@Peter "R" != "T" You mean EROPS. Also known as "Engines Running/Turning Or Passengers Swimming".

@Monolo -- ETOPS nowadays is basically a catchall for all the things required to fly over an area with no diversion options nearby.

@paul Yes and No, it's ambiguous!? I'm not a pilot! I refer to the old use of EROPS ("Extended range operations"), till mid 1980s. And the old usage of ETOPS ("Extended Range Operations with two-engine airplanes") till 2007. Airbus suggessted LROPS ("Long Range Operations",  especially for three- and four-engine to avoid confusion, particularly for those operations beyond 180-minutes diversion time. Finally the FAA decided to stay with ETOPS but use it for every plan, so it's current official meaning is "Extended operations" (no mention of "twin").

It isn't that new aircraft require a certain number of minutes, it is that they chose to certify it to a certain number of minutes and went through the approval process to have it certified to a particular set of standards.

@Lnafziger Boeing states "With this approval, required for four-engine passenger airplanes built after Feb. 2015 [...]" and "ETOPS [...] regulations have recently been applied to the design of passenger airplanes with more than two engines."

ETOPS: Engines Turn or Passengers Swim!

@collector They worded it in an ambiguous way in the article. It is required IF you want to fly more than a certain number of minutes from a suitable airport, however it is still an option for the manufacturers (although it would be very foolish for them not to do so).

I was unaware that ETOPS applied to any four engine jet.  Glad this question was asked.

@Peter: right, but the beginning of the Wikipedia article page is still causing confusion. It should give the current definition. The historical definitions and proposals can go in the History portion.

Well ETOPS is an extended Range Twin Operations approval (ETOPS) permits twin-engined aeroplanes to operate over a route that contains a point further than one hour flying time at the approved one-engine inoperative cruise speed. This is applicable to flights under standard conditions in still air from an adequate aerodrome.

ETOPS stands for Extended-range Twin-engine Operational Performance Standards, a rule which permits twin engine aircrafts to fly routes which, at some point, is more than 60 minutes flying time away from the nearest airport suitable for emergency landing. ETOPS may also be interpreted as Engines Turn or Passengers Swim.
It is not a rule which applies after an engine has failed. Rather, it is a set of regulations and standards which must be met if an airliner wishes to fly its planes more than 60 minutes away from a suitable emergency airport.
History
Early combustion engines were noticeably unreliable. It was not uncommon for a 4-engine piston aircraft to arrive at its destination with only 3 engines running. Twin engine aircrafts, as a result, were required to fly dogleg paths to stay close enough to an adequate airport.
Aircrafts with more than 2 engines were not restricted by this rule. Thus, many transatlantic flights were flown with Boeing 747s and L-1011s, since airliners can fly a more direct route with these aircrafts.
As engineers gained more experience in jets, they slowly recognized that jet engines are much more reliable than their piston counterparts. The FAA began to approve flying twin engines 120 minutes away from a suitable airport. This made twin engine aircrafts popular, because the fuel efficiency of flying a twin is much better than flying a 4-engine 747 or A340.
Certification
ETOPS certification requires both the aircraft and the airline to comply with a set of standards.
For the aircraft, the manufacturer must demonstrate that flying with only one engine is relatively easy for the flight crew, safe for the airframe, and an extremely remote event.
The airline must demonstrate that its flight crew training and maintenance procedures are up to a higher standard. Pilots, engineers and staff must be specially qualified for ETOPS.
Recently, more operators are adopting the ETOPS approach to non-ETOPs routes. They discovered that the approach offers significant improvements in reliability, performance and dispatch rates. The cost of application is later offset by reduced maintenance costs, and costs associated with diversions, delays and turn backs.
Flight Plan
An ETOPS flight plan may look something like this:

Let's say the aircraft's ground speed (with one engine inoperative!) is 450 knots. By drawing circles with radius 450nm around alternate airports, we can obtain areas which the flight must stay within. The flight path always stays inside one of these circles. If we are operating under ETOPS 120, we will draw the circles at 900nm.
Actual flight plans are slightly more complex, since winds aloft (sometimes more than 100 knots) will affect the aircraft's ground speed. Dispatchers use software to calculate a route, taking aircraft weight, fuel consumption and winds into consideration.

Good answer. I would like to know why the 747-8 didn't get a higher ETOPS. And if the 747-400 can fly ETOPS 330+ routes. Maybe I should ask a new question about that.

why it didn't get higher? The 747-400 is not restricted to ETOPS, effectively it's ETOPS infinity. For the 747-8, it has to be a number rather than unlimited.

So say an airline wanted to fly Cape Town - Auckland. It could do it with a 747-400 or A350, but not a 747-8?

I would suggest asking "why does ETOPS apply only to newly built 4 engines aircrafts" as a new question.

Actually, this answer is based on the old rules. it now does apply to 3 and 4 engine aircraft, and has a new name which isn't restricted to twin engine aircraft.

This answer doesn't seem to address the fact that a 747 has four engines at all

I see no mention of 14CFR 121.161 so here it is.

§ 121.161 Airplane limitations: Type of route.
(a) Except as provided in paragraph (e) of this section, unless
  approved by the Administrator in accordance with Appendix P of this
  part and authorized in the certificate holder's operations
  specifications, no certificate holder may operate a
  turbine-engine-powered airplane over a route that contains a point—
(1) Farther than a flying time from an Adequate Airport (at a
  one-engine-inoperative cruise speed under standard conditions in still
  air) of 60 minutes for a two-engine airplane or 180 minutes for a
  passenger-carrying airplane with more than two engines;
(2) Within the North Polar Area; or
(3) Within the South Polar Area.
(b) Except as provided in paragraph (c) of this section, no
  certificate holder may operate a land airplane (other than a DC-3,
  C-46, CV-240, CV-340, CV-440, CV-580, CV-600, CV-640, or Martin 404)
  in an extended overwater operation unless it is certificated or
  approved as adequate for ditching under the ditching provisions ofpart
  25 of this chapter.
(c) Until December 20, 2010, a certificate holder may operate, in an
  extended overwater operation, a nontransport category land airplane
  type certificated after December 31, 1964, that was not certificated
  or approved as adequate for ditching under the ditching provisions
  ofpart 25 of this chapter.
(d) Unless authorized by the Administrator based on the character of
  the terrain, the kind of operation, or the performance of the airplane
  to be used, no certificate holder may operate a
  reciprocating-engine-powered airplane over a route that contains a
  point farther than 60 minutes flying time (at a one-engine-inoperative
  cruise speed under standard conditions in still air) from an Adequate
  Airport.
(e) Operators of turbine-engine powered airplanes with more than two
  engines do not need to meet the requirements of paragraph (a)(1) of
  this section until February 15, 2008.
[Doc. No. 7329, 31 FR 13078, Oct. 8, 1966 as amended by Amdt. 121-162,
  45 FR 46739, July 10, 1980; Amdt. 121-251, 60 FR 65927, Dec. 20, 1995;
  Amdt. 121-329, 72 FR 1879, Jan. 16, 2007]

Why the ditching-certification exemptions for all those old propliners?

Those exemptions went away 12/20/2010 and I suspect they had something to do with Alaska operations which is a whole other thing unto itself.

ETOPS does not only affect the engines of an aircraft – long ETOPS ratings such as the 747-8's 330-minute ETOPS capability also require that systems like fire suppression be sufficient for over five (!) hours of flying after something in the cargo hold sets itself ablaze.  This is accomplished by metering a flow of extinguishing agent into the cargo hold after the initial "knockdown" shot to keep the fire in check until the plane can land.

Boeing has a post about it here: http://www.boeing.com/commercial/aeromagazine/articles/qtr_2_07/article_02_7.html
Basically, twins have to get ETOPS when they are more than 60 minutes from an airport, and planes with 3+ engines have to get it when they are more than 180 minutes from an airport.
Hopefully that answers your question.

Easy to remember like this:
Engines
Turn
Or
Passngers
Swim
Basically it is a rule governing all twin engine aircraft. Before there was the 777/787 - when twin engine aircraft were not capable of flying trans-atlantic or trans-pacific routes while still being within a 60 minute window of being able to perform an emergency landing at the nearest airport, twin engine aircraft were forbidden from making such flights. Now, a plane can be ETOPS certified to a very high standard, one which used to only be achieved by 3 or 4 engine aircraft. The standard is to prove the plane can fly over vast stretches of ocean and in the worst possible situation still be able to have enough range to land within 60 minutes without ditching in the water.

Welcome! that's correct, but doesn't add new elements to existing answers.

"have enough range to land within 60 minutes" - except ETOPS > 60 where the plane must be capable of flying for more than 60 minutes to make it to a diversion airport or its final destination.


text:
Why does ETOPS not apply to older 4 engine aircraft?
This is a follow-up to my previous question: What is ETOPS and how does it work?
There is a related question here, but it does not specifically answer this new question.
Facts:

Since February 2015, all new aircraft are required to get ETOPS
approval to fly ETOPS 180+ routes. Source.
The 747-8 has ETOPS 330. The 787 has ETOPS 330. The A350 has ETOPS
370.

Why does ETOPS not apply to the 747-400?

Perhaps with the ever-increasing range of new aircraft it became more relevant...

I think it's because the last 747-400 was built in 2009.

§121.162   ETOPS Type Design Approval Basis.
Except for a passenger-carrying airplane with more than two engines manufactured prior to February 17, 2015 and except for a two-engine
  airplane that, when used in ETOPS, is only used for ETOPS of 75
  minutes or less, no certificate holder may conduct ETOPS unless the
  airplane has been type design approved for ETOPS and each airplane
  used in ETOPS complies with its CMP document as follows:
(a) For a two-engine airplane, that is of the same model
  airplane-engine combination that received FAA approval for ETOPS up to
  180 minutes prior to February 15, 2007, the CMP document for that
  model airplane-engine combination in effect on February 14, 2007.
(b) For a two-engine airplane, that is not of the same model
  airplane-engine combination that received FAA approval for ETOPS up to
  180 minutes before February 15, 2007, the CMP document for that new
  model airplane-engine combination issued in accordance with
  §25.3(b)(1) of this chapter.
(c) For a two-engine airplane approved for ETOPS beyond 180 minutes,
  the CMP document for that model airplane-engine combination issued in
  accordance with §25.3(b)(2) of this chapter.
(d) For an airplane with more than 2 engines manufactured on or
  after February 17, 2015, the CMP document for that model
  airplane-engine combination issued in accordance with §25.3(c) of this
  chapter.
§25.3   Special provisions for ETOPS type design approvals.
(a) Applicability. This section applies to an applicant for ETOPS type
  design approval of an airplane:
(1) That has an existing type certificate on February 15, 2007; or
(2) For which an application for an original type certificate was
  submitted before February 15, 2007.
(b) Airplanes with two engines. (1) For ETOPS type design approval of
  an airplane up to and including 180 minutes, an applicant must comply
  with §25.1535, except that it need not comply with the following
  provisions of Appendix K, K25.1.4, of this part:
(i) K25.1.4(a), fuel system pressure and flow requirements;
(ii) K25.1.4(a)(3), low fuel alerting; and
(iii) K25.1.4(c), engine oil tank design.
(2) For ETOPS type design approval of an airplane beyond 180 minutes
  an applicant must comply with §25.1535.
(c) Airplanes with more than two engines. An applicant for ETOPS
  type design approval must comply with §25.1535 for an airplane
  manufactured on or after February 17, 2015, except that, for an
  airplane configured for a three person flight crew, the applicant need
  not comply with Appendix K, K25.1.4(a)(3), of this part, low fuel
  alerting.

Very interesting. That also means that the 747-8s built before February 17, 2015 are not required to comply with ETOPS. They must be slightly more valuable (than they would have been) as a result.

In a lot of safety regulations (not just aviation) there is a concept of "grandfathering". Regulators want to tighten safety regulations but they feel that doing so for exiting vehicles would be an undue burden.


text:
What prevents a passenger from hijacking a private jet?
I was reading another question on this site when I saw this answer.
As you can see in the photo I copied below, this private jet has no cockpit door. On commercial aircraft the bullet-proof cockpit door is seen as the last line of defense against would-be hijackers.
What security measures are in place to prevent unauthorized passenger access to the controls of private jets? Even though they are smaller and carry fewer people, a G650 or BBJ pointed in the wrong place can do a lot of damage.

The same thing that prevents someone from hijacking a bus: Nothing. (or, possibly, morals if you want to get into a philosophical discussion)

So why are the doors on commercial aircraft bullet-proof?

This is very close to being a duplicate of this question

@Pondlife I had seen that question. I feel that that question relates to the pre-boarding security. While my question explicitly deals with onboard security.
I find it to be more of a duplicate of this questionBut I feel that question is asking if you can charter and fly a plane yourself from the start. While I'm asking about inflight hijacking from a passenger.
I'll delete people feel this is a duplicate.

@collector Yes, that's why it's only "close" :-) But if pre-boarding security is limited then on-board security is more difficult, so there is some connection.

@Blam You are right, this is getting out of hand. I have done the same.

In reference to a deleted comment that is pertinent to the discussion, "private" jets are only private when not being used for commercial purposes.  This same jet may be operated commercially, and the regulations do not require them to have a hardened door (or even a door at all) unless it is operated by a 121 carrier (airline).  The size of the aircraft and the scope of operation also factors in to the rules.

Nothing.  That's why smart pilots carry guns.

Plus, the cockpit in that type of plane is an amazingly small space to attack a determined and seat belted pilot with nothing to lose. The hijackers would have to know how to fly the plane. In which case, why hassle with belligerent pilots. Just steal the plane on the ground. Door issue solved.

the Second Amendment comes to mind!

The same thing that prevents the passengers in your car from hijacking it and using it to run people down or drive it through a mall:  It's your private car and you generally know the people that you let in to it.
The same applies to private aircraft.

I would say it's easier to do more damage with a normal jet than a normal car, given you don't care whether you'll see the next sunrise.

@collector While that may or may not be true (private individuals may own all kinds of destructive things, including heavy machinery, monster trucks, and even tanks), in practice this is how it works and how the laws are written. The PIC is responsible for the safety of the aircraft and those on board.

Just to bring things into perspective: Strategically impacting three BBJs (or G650s) into a cruise ship (Allure of the Seas) can cause a lot of damage. I doubt you can do this much damage with a herd of monster trucks.

@collector The Oklahoma City Bombing is but one example of what you can do with one box truck....  People can turn all manner of things into extremely destructive objects.

@collector Also, there are  more regulations that govern bigger airplanes such as an airbus that is being privately operated. It's more about the size (actually weight) of the aircraft than how it is being operated.

The OKC bombing required a truckload of explosives. You would be surprised how little, comparatively, the useful load of a jet like the one pictured is. It’s only advantage is the velocity at which it can deploy its mass, and the difficulty to defend against it. If the Allure of the Seas was docked, and the monster trucks could get to it, they could do maybe not quite as much, but almost as much destruction. And, the monster trucks can carry dangerous cargo.

What security measures are in place to prevent unauthorized passenger access to the controls of private jets?

None. The passengers outnumber the pilots, and unlike commercial jets are not outnumbered by passengers who prefer the original scheduled route to the new one.
It would also be very easy to arrange pickup at a quiet airstrip, kill the crew, stuff the bodies in a car trunk and do the whole flight without them.
The reason this isn't much of a concern is because small jets have neither the mass nor fuel capacity to do anywhere near the amount of damage possible with an airliner. As an example, when I was in college a light aircraft hit a building on approach to the airport, and nobody noticed. The building was the city hospital, the plane struck an empty floor and sat there with the tail sticking out. ATC wondered where it went, asked the next inbound to have a look, and then phoned the building. Staff went to the appropriate room and extracted the injured (but not dead) pilot and passengers.

Wow, do you have a link to the NTSB report for that accident?

A 737 BBJ is roughly the same size as a commercial 737. And it has additional fuel tanks.

@pericynthion Could be this report from a newspaper

@collector that's a 3rd-party reprinting (Eugene OR is 1300km from Edmonton) , but yes it is the event I described. Maybe the Edmonton Journal hasn't scanned it's archives.

@collector a 737 doesn't normally qualify as a "private jet"

They crashed into the right place...

@paul Boeing makes business jet variants of all their aircraft, including the 747-8. https://www.boeing.com/commercial/bbj/ Plenty of 737 BBJs out there; https://en.wikipedia.org/wiki/Boeing_Business_Jet says 159 in service. 9 747s, too.

The difference in security measures is due to the difference in the passengers.
Commercial airlines could carry almost anyone as passengers. Although some amount of security is done on the ground, and in the air, a cockpit door is still a useful line of defense. It's difficult to verify the intentions or capabilities of everyone that will ever be a passenger on the plane. Also, aside from limited circumstances, there is no reason for anyone from the cabin to be accessing the cockpit.
Private jets are different, because they are just that; private. A business or individual has the responsibility to clear their passengers before a flight. If they feel that there may be an issue, they can certainly have a cockpit door. But that situation is not normal. On a private jet, the passengers may comprise of the owner and his or her guests. As a matter of courtesy they may want to visit the cockpit. On a business flight, the circumstances would be similar.
As paul pointed out, these planes typically don't have the range or size to be capable of the same things an airliner would be. And the larger the plane, the larger the price tag. This would cost much more than just a commercial ticket, which also serves as a form of security.
Large jets will also have additional security added: What are the security measures preventing someone from chartering a 747 and using it to commit a terrorist attack?

In your picture, the door is currently open.  It is most definitely there, but probably not re-enforced as commercial airline doors are.
Very little physically prevents a passenger from entering the cockpit on a private charter.
Generally, with private planes, security is done on the ground.  The charter company does whatever diligence they feel is necessary to know their guests and their intentions before boarding.
Commercial airlines obviously cannot do extensive checks on all their passengers, but they do cross-check against lists like the No-Fly list.

In the other answer linked in the question (where I got the picture), a pilot who flies this type of plane says that there is, in fact, no door.

Why are you discussing a charter company in a question about private jets? ;-)

@collector Some do and some don't.  Some of them it's a curtain, some are wood, but they aren't normally reinforced like what is required of an airliner.

While secured cockpit doors are not required on chartered or corporate aircraft,  they do have a few security measures which are the same as those found on airliners to deter criminal activity or hijacking by passengers aboard the aircraft:
Security screenings:  Large aviation charter companies will subject travelers to TSA screenings, involving metal detectors and x-ray luggage that they carry board.
Higher class clientele: Travelers aboard private jets and charted aircraft generally are wealthy individuals, or well-connected ones usually are not up for causing that kind of major crime aboard an aircraft.
Traveler reputation amongst charter companies: as mentioned earlier large scale criminal activity by most private jet flyers is rare.  But there can be cases of obnoxious passengers being rude or abusive with the flight crews and causing minor property damage. This is particularly troublesome with celebrities, musicians, professional athletes, etc.   That kind of antisocial behavior will be quickly curbed as such people develop a reputation amongst flight crews and charter companies, who have quite long and vivid memories. The bottom line is if you don’t want to travel by car, bus, or amongst other “little people” on an airliner, be kind to your flight crews and they’ll be kind to you.
The fear of the Law:  Causing trouble aboard an aircraft or anything that could be interpreted as a violation of FAR 91.13 can carry sentences of up to 10 years in prison, and fines as great as $250,000.   Aircraft hijacking is a capital offense under the US code.
Flight crews pack heat:  Yes some of them are armed with guns and will shoot you if they believe you are an immediate threat to the aircraft or other passengers.

To prevent business jet or charter flight hijacking from private jet terminal or Fixed Base Operator (FBO) are very difficult because

Passengers are company valuable passengers or millionaire. So the intention to hijack or suicide is quite low except mental disorder.- Detection by observe the Suspicious behaviors of Passengers.
Prevention can be done only on-ground because normally private jets have no cockpit door and operate with 2 pilots. If access control to airside is less strict. Prohibited articles, weapons, narcotic etc. can be smuggled by private jets.- Detection is strict control to airside by random and unpredictable security measures as per Annex 17 - 9th edition.
Risk assessment and intelligence are the key.

You would be surprised how common weapons are on private, business, and chartered aircraft. Especially during hunting season. None of the things you mentioned are prohibited on flights, necessarily. If general possession is prohibited by federal or local law, then passengers have to follow that law. Even if the law is different at their destination versus their departure airport. Just ask Snoop Dogg.  The PIC MUST prohibit anything that is a danger to flight or anyone that is under the influence of drugs or alcohol. But, they can also allow things that airlines don’t. Their call.

Something like this actually did happen in 1994, although it was a cargo aircraft and not private: FedEx 705
A soon to be fired FedEx employee riding on a cargo DC10 tried to take over the flight and kill the flight crew by attacking them with a hammer and a speargun, so he could crash the plane. Being a cargo flight with only company employees on board, typical commercial safeguards were not in place, nor was the flight deck secured.
After a bloody fight, and some radical maneuvers to unbalance the attacker by the copilot, who was partially disabled due to a fractured cranium (had the DC10 almost inverted at one point), the attacker was subdued and the flight landed safely despite the impaired condition of the pilots and also being 16 tons overweight.
All of the flight crew survived, although none ever flew commercially again, due to cranial injuries from hammer blows.
In this case, the bravery and fortitude of the flight crew stopped a potential disaster.

Money prevents the hijacking.
Hijackers generally can’t afford to charter a private jet like the one shown. And, people with the money to be able to afford that type of flight can afford to go wherever they want on a regular airline flight anyway. If the passenger is the pilot’s boss, and the boss says to change the destination mid-flight, it’s not hijacking. It’s customer service. Otherwise, how would an unauthorized person get on the plane without the pilots’ knowledge?
Now, kidnapping is another story. But, that would entail kidnapping the pilots before they even get to the plane. Or rushing the plane while it’s on the ground. Then, the hijackers would be putting their lives and the success of their plan in the hands of one or two desperate pilots with nothing to lose.
And, theft would make any cockpit door pointless and arbitrary.

You got it wrong. Bin Laden was a rather wealthy person, he could have BOUGHT several private jets to use in the 9/11 attacks. Other hijackers have had close ties with national governments (Iran, Libya, to name but two) that definitely have such funds. The real reason is that the passengers are the people who typically own the aircraft already, or their personal guests.

You are correct sir. Bin Laden was a rare case. And, national governments would not want the paper trail. We do still have a pretty strong military and hair triggered leadership. A governmentks plausible deniability would be important to them. Both of these scenarios makes the security door a moot point. Just like in theft. And, the vast majority of the passengers of the business and charter jets at our airport are not owners.


text:
What's the process for an uncontrolled airfield to become controlled/towered?
I know some uncontrolled airports can have more operations per day than many controlled airports. That got me wondering what the process is for the change to a towered, controlled airport. I know a control tower was recently built (2005) at Provo, UT (KPVU) which is the second busiest airport in Utah.

Is there simply a threshold of average operations/day? Do the number of accidents and incidents come into play?
Does the FAA start the process or does the community have to lobby for the tower?
Who pays for the tower, is it all federal FAA funds or does the state and city where the airport is located pay?
Are there any US airports where towers are being built or considered? Given the recent sequestration and how close we came to having over 100 towers shut down, I'm guessing any current plans are on hold.

Here is a case from my youth I remember at an airport near me.  Here our Senators had to get the money from Congress appropriated, while the FAA was not behind the project.
http://articles.latimes.com/1988-05-01/local/me-3114_1_whiteman-airport
Appears the process, at lease back in 1988, involved politics between local leaders and the FAA, ( recent incidents as well as traffic levels considered)

Good article, thanks. "The FAA recommends a control tower if at least 200,000 yearly takeoffs and landings occur". I'm sure there's more criteria than just operations/year, some class B airports might not exceed 200,000 ops/year.

@GeoffreyGallaway You are right, KCLE, KMSY, KMCI, and KPIT all have less than 200,000 operations per year.  (The lowest is KMCI  with 129,489.)

I finally found an AOPA article that discusses requirements for a control tower.
They say:

The FAA has the authority to establish control towers or discontinue
  control tower services through the National Airspace System when
  activity levels and safety considerations merit such action.

In order to open a new tower, there must be a positive Benefit-Cost ratio (which is a complicated thing to calculate).  The FAA typically pays for the cost, and here is the criteria that they list:

Criteria
According to FAR Part 170.13, the following criteria, along with
  general facility establishment standards, must be met before an
  airport can qualify for a control tower:

The airport, whether publicly or privately owned, must be open to and available for use by the public as defined in the Airport and
  Airway Improvement Act of 1982;
The airport must be part of the National Plan of Integrated Airport Systems;
The airport owners/authorities must have entered into appropriate assurances and covenants to guarantee that the airport will continue
  in operation for a long enough period to permit the amortization of
  the control tower investment;
The FAA must be furnished appropriate land without cost for construction of the control tower; and
The airport must meet the benefit-cost ratio criteria specified herein utilizing three consecutive FAA annual counts and projections
  of future traffic during the expected life of the tower facility. (An
  FAA annual count is a fiscal year or a calendar year activity summary.
  Where actual traffic counts are unavailable or not recorded,
  adequately documented FAA estimates of the scheduled and nonscheduled
  activity may be used.)

The FARs specifically state that an airport is not guaranteed to
  receive a control tower, even if the airport meets all the criteria
  listed above. This is where the contract tower program comes in. The
  FAA, responding to an airport sponsor's request for an air traffic
  control tower, can elect to establish a contract tower. The FAA can
  either elect to pay for the service in its entirety, or enter into a
  cost-sharing agreement with the sponsor, depending on the results of
  the benefit-cost analysis. Typically, the airport sponsor is
  responsible for 10 percent of the cost of construction and operations.

For the Benefit-Cost calculation, they use the following criteria:

Site-specific activity forecasts are used to estimate three categories
  of tower benefits:

Benefits from prevented collisions between aircraft.
Benefits from other prevented accidents.
Benefits from reduced flying time.

Explicit dollar values are assigned to the prevention of fatalities
  and injuries and time saved.
Tower establishment costs include:

Annual operating costs: staffing, maintenance, equipment, supplies, and leased services.
Investment costs: facilities, equipment, and operational start-up.

The article contains a lot more information, along with links to the relevant regulations, etc.


text:
Why is Schaumberg Airport (06C) in Chicago an uncontrolled field?
Schaumburg Airport lies underneath some of the busiest airspace in the world and is 8 miles west of Chicago O'Hare, one of the most active airports in the US. It's not the busiest uncontrolled field in the US, but it gets more traffic than some towered airports. Given the location, airspace complexity, and airport popularity why is Schaumburg an uncontrolled field?

Its under the 1900 foot shelf, and right next to the 3000 foot shelf. O'Hare ATC won't route traffic under the shelf so it shouldn't cause any kind of factor to safety or routing, ORD traffic should be no factor unless you bust overlying Class-B. It's not really "complex" airspace, since you are flying under the Class-B shelf you are not in Class-B airspace. The only thing really complex about it is being within the Mode-C veil.

It should also be noted that there are no published instrument procedures into 06C, so you won't encounter traffic under ATC control coming in on an instrument approach like you would at Executive or DuPage.

Alternatively, ask why should it be controlled? The runway is 3800' and there are no instrument approaches; that limits the traffic you'll get in there to smaller, slower aircraft. As @RonBeyer explained, the airspace isn't complex or challenging. And adding a tower would require a lot of coordination between the new tower and KORD controllers, and perhaps procedural changes at KORD depending on the design of the class D (?) airspace. So if there's no pressing need for a tower (e.g. persistent airspace or safety issues) it seems like a lot of effort for little benefit.

@Pondlife Please make that an answer.

Most likely, the airport was formed in the early-mid part of the 20th century as a small country airport outside of the Chicago metro area.  The city grew around it, similar to Compton-Woodley airport in Los Angeles or Cross Keys or Camden Co. in the Philadelphia metro area.  With the introduction of the modern airspace systems for commercial air travel the Class B shelves covered these airports but did not include them.


text:
Is there a conventional notation or name for the slip angle?
Angle of attack is usually designed by alpha (as in alpha_prot).
Is there such a conventional notation or name for other axes? I'm particularly interested in the slip angle.

Sideslip angle is commonly notated as β (see e.g. https://en.wikipedia.org/wiki/Slip_(aerodynamics)).

There is only one other such angle. It is indeed the sideslip one, and its standard greek letter is $\beta$ (beta)


text:
Do auto-flaps exist?
Slats can be extended automatically depending on dynamic air pressure. Fly-by-wire systems provide flight envelop protection when flaps/slats are extended but I cannot find any reference of fly-by-wire feature such as auto-retractation/extension of flaps/slats depending on angle of attack or air-speed.
Do systems to automatically retract/extend flaps depending on flight conditions (speed, angle of attack,dynamic pressure,...) exist?

It can be much simpler than that.
The aerobatic glider Mü-28 has a symmetric airfoil with 20% flaps, and those flaps are automatically set as a function of the g-load experienced near the center of gravity and the dynamic pressure. Basically, a spring-suspended lever with a mass at the end creates the necessary control input. In straight flight they are deflected downwards which makes the airfoil more suitable for gliding, in a zero-g parabola or in a knife-edge flight they are moved to 0° deflection, and in inverted flight they show a negative deflection angle. If flight speed increases, the deflections become proportionally smaller, thus preventing overloading the airframe (which is dimensioned for ±10g, so overloading it is hard anyway).

Mü-28 in inverted flight (picture source). Thanks to the low sun the rear part of the fixed wing section is illuminated so the negative flap deflection is easy to discern.
From this page:

This innovative automatic flap system fitted to the Mü28 was developed
  at the Flugwissenschaftliche Vereinigung Aachen under the project
  designation FVA-21, controlling the position of the flaps, depending
  on the speed and the load factor, so that the aircraft flies with
  optimal angle of attack in all flight conditions.

Scheduling the maximum deflection angle with dynamic pressure as an overload protection can thus be done in two ways:

Fully mechanically by adding a spring element in the flap linkage.
In a fly-by-wire control system by hard-coding it into the control laws. For faster airplanes this is preferred as it does not require a spring in the system - any elasticity will at some point cause flutter, this is only a question of speed.

Automatic flap control systems do exist. Boeing uses a system called Trailing edge load relief system, that automatically retracts flaps in case of excess airspeed. From ATSB  Report 200202710:

Flap load relief system
The flaps/slat electronics unit provided a trailing edge flaps load relief function that protected the flaps from excessive air loads. That function was operative at the FLAP 30 and FLAP 40 positions only. The flap lever did not move, but the flap position indicator displayed flap retraction and re-extension.
When the flaps were set at FLAP 30, the trailing edge flaps:
• retracted to FLAP 25 if the airspeed exceeded 176 kts
• re-extended when the airspeed was reduced below 171 kts
When the flaps were set to FLAP 40, the trailing edge flaps:
• retracted to 30 if the airspeed exceeded 163 kts
• re-extended when the airspeed was reduced below 158 kts

Boeing 787 and Airbus A350 have systems that automatically adjust wing camber in flight using flaps to reduce drag. The Boeing system is called trailing edge variable camber (TEVC).
Of course the flaps are controlled by the computer in a number of combat aircraft.
Actually automatic flaps are not new. The Breguet XIV had them in the lower wing. Basically, the flaps (called 'Equalizer flaps') were hinged to the rear spar and were maintained at a given angle using rubber cords, which permitted them to vary with wind pressure.


text:
Is there a complete source for aircraft registration information?
I am building an app that requires access to commercial aircraft registrations, in the UK to begin with and then more global as I start to expand the service.
I have found this CAA site which works for now, but I would like to include all registered aircraft.

http://www.airframes.org/ Is a good bet. I do not know if they offer some sort of API access.

@J.Hougaard An interesting source, but not for other-than-personal use. From the about page on airframes.org: "The use of this database is free of charge for occasional (low-volume) personal lookups by private users by means of a standard web-browser. [...] It is not allowed to collect and transfer these data anywhere else. Copyright rules apply."